1. Field of the Invention
This invention relates generally to glass fiber mats, polymeric laminates reinforced with the same, and in particular thermoplastic laminates and methods for making the same.
2. Technical Considerations and Prior Art
An increasingly popular process for forming composites is by compression molding or stamping a moldable sheet of a thermoplastic resin reinforced with fibers such as a glass fiber mat, often referred to as glass mat thermoplastics or xe2x80x9cGMTxe2x80x9d. These composite sheets can be used to form articles such as automobile components and housings for computers.
An example of a commercially successful GMT sheet is the AZDEL(copyright) moldable composite sheet which is formed by extruding layers of polypropylene resin sheet with needled mats of continuous glass fiber strand. The AZDEL(copyright) composite sheet is commercially available from Azdel, Inc. of Shelby, N.C.
U.S. Pat. No. 3,044,146 discloses a fibrous glass reinforcing mat which utilizes a limited quantity of continuous glass strands to maintain major components of weakly bonded fibrous glass material in evenly distributed, more integrated form. The unwoven fibrous bodies are tied together by continuous strands of glass fibers and interconnect through the bodies at regularly spaced intervals.
U.S. Pat. No. 3,614,936 discloses a nonwoven structure of chopped glass strand which is stitched together. Optionally, the nonwoven structure can include parallel glass strands lengthwise of the structure. The stitched nonwoven structure can be compacted with heated rollers to fuse the stitching thread and then needled.
U.S. Pat. Nos. 3,664,909; 3,713,962 and 3,850,723 disclose fibrous mats of unstranded filaments which can be layered with reinforcing mats of fiber strands.
U.S. Pat. No. 4,749,613 discloses a thermoplastic stampable sheet composed of 30 to 80 percent by weight reinforcing fibers arranged in one direction, needled together with a swirled continuous strand mat, the sheet being impregnated with a thermoplastic resin.
U.S. Pat. No. 4,931,358 discloses a material consisting of a thermoplastic polymer and a needled textile fabric consisting of at least two layers of continuous filament yarn oriented in at least one preferred direction and at least one layer of unoriented fibers.
U.S. Pat. Nos. 4,948,661; 5,011,737; 5,071,608 and 5,098,624 disclose fiber reinforced thermoplastic molded products produced by intimately blending reinforcing glass fibers and thermoplastic fibers into a web and heating the web to the melting point of the thermoplastic fibers while applying pressure to the web to press the web into a consolidated structure.
U.S. Pat. Nos. 5,108,678 and 5,194,462 disclose a fiber reinforced plastic sheet having a gradient layer structure wherein less opened strands are concentrated in the lower layers and more opened strands are concentrated in the upper layers of the structure.
U.S. Pat. Nos. 5,129,131 and 5,540,986 disclose a stampable sheet of thermoplastic resin reinforced with a glass fiber mat having a layer of non-oriented fibers and a layer of unidirectional fibers which are mechanically intertwined.
There is a long-felt need in the industry for a mat for applications such as GMT which can be readily impregnated by the thermoplastic matrix material, which has good uniformity of glass distribution and flow into complex mold shapes and which provides a composite having mechanical properties, such as strength and stiffness and good surface smoothness throughout its entire surface. However, the inability to thoroughly impregnate the mat with resin, especially unidirectional continuous strand along the longitudinal edge of the mat, results in poor surface finish in laminates incorporating the mat. This in turn detracts from the aesthetics of a molded product fabricated from the laminate.
It would be advantageous to provide a mat for applications such as GMT and other molding processes which provides a consistently high quality finish over the entire surface of laminates and products incorporating the mat.
The present invention provides a mat having at least one primary area and at least one secondary area and adapted to reinforce a polymeric matrix material, the mat comprising (a) a first layer comprising a plurality of generally parallel, essentially continuous glass fiber strands oriented generally parallel to a longitudinal axis of the mat, at least a portion of outer surfaces of the first layer glass fiber strands having applied thereon at least a partial layer comprising at least a partially dried residue of first coating composition which is compatible with a polymeric matrix material, wherein at least a first portion of the first layer glass fiber strands are positioned within the at least one primary area at a primary strand density and at least a second portion of the first layer glass fiber strands are positioned within the at least one secondary area at a secondary strand density which is different from the primary strand density; and (b) a second layer comprising a plurality of randomly oriented glass fiber strands positioned within the at least one primary area and the at least one secondary area and adjacent to a surface of the first layer, at least a portion of outer surfaces of the second layer glass fiber strands having applied thereon at least a partial layer comprising at least a partially dried residue of a second coating composition which is compatible with the polymeric matrix material, wherein the first and second layers are joined to hold the mat together.
Another aspect of the present invention is a reinforced polymeric laminate comprising a polymeric matrix material and the reinforcing mat described above.
Yet another aspect of the present invention is a reinforced polymeric composite comprising at least one laminate comprising a polymeric matrix material and the reinforcing mat described above.
Another aspect of the present invention is a method for making a mat adapted to reinforce a polymeric matrix material, the method comprising the steps of (a) positioning a plurality of generally parallel, essentially continuous glass fiber strands oriented generally parallel to a longitudinal axis of the mat to form a first layer, at least a portion of outer surfaces of the first layer glass fiber strands having applied thereon at least a partial layer comprising at least a partially dried residue of a first coating composition which is compatible with a polymeric matrix material, wherein at least a first portion of the first layer glass fiber strands are positioned within an at least one primary area at a primary strand density and at least a second portion of the first layer glass fiber strands are positioned within an at least one secondary area at a secondary strand density which is different from the primary strand density; (b) dispersing a plurality of randomly oriented glass fiber strands within the at least one primary area and the at least one secondary area and adjacent to a surface of the first layer to form a second layer, at least a portion of outer surfaces of the second layer glass fiber strands having applied thereon at least a partial layer comprising at least a partially dried residue of a second coating composition which is compatible with the polymeric matrix material; and (c) joining the first and second layers to hold the mat together.
Still another aspect of the present invention is a method for reinforcing a polymeric matrix material to form a reinforced laminate, the method comprising the steps of making a mat in a manner as described above, coating and impregnating at least a portion of the mat with the polymeric matrix material and at least partially curing the polymeric matrix material to form a reinforced laminate.